In a video communication field, especially in a videoconferencing system, usually it needs to transfer desktop information, such as films or file information, to the remote video communication terminal at the same time while a local image such as an image taken by a video camera is transferred, to a remote video communication terminal.
There are two solutions for the above requirement. The first solution is as follow: projecting desktop information of a PC by a projector, capturing the projected image by the video camera of a videoconference terminal and then sending to the videoconference terminal, transferring the desktop information to a remote video communication terminal after processing. The second solution is as follow: transforming the desktop information to a standard PAUNTSC (Phase Alternating Line/National Television System Committee) format signal by a VGA (Video Graphic Array) converter, inputting the PAUNTSC format signal to the videoconference terminal as one of the video source signals, then transferring the desktop information to a remote video communication terminal after processing by the videoconference terminal.
Although, the above solutions are simple and real-time, but there are some disadvantages so that transmission of desktop information of a PC cannot be solved perfectly. In the first solution, to keep higher clarity the visual part of the captured image becomes smaller, i.e. the desktop information cannot be wholly transferred at a time. In the second solution, there is a loss during converting a digital signal to an analog signal in the VGA converter, so that clarity of all images that pass through the VGA converter decreases greatly; although clarity can be raised slightly by partly amplifying desktop information and then transferring to the remote terminal, but it is complicated in operation and quality of the reproduced image is still unsatisfied.